@Zardnaar
FYI, I made a somewhat complex sandwich for lunch: toasted onion roll, mayo, spicy brown mustard, thinly sliced radish, garlic sprouts, pickled red onions, ham, mortadella and feta cheese. No pix.
Still, I can say your instincts were dead on target! Mortadella and feta pair VERY well. It’s officially a combination I’m storing in my long term sandwich-making mental folders.
I’m almost out of mortadella at this point. Only enough for one more sandwich. Next time I get some, I may aim at more of a Mediterranean approach. Some salami. Oil & red wine vinegar as opposed to mayo. That kind of thing.